bright sphere bullet: for space ship shooter

Hallo guys

I’m try to understand what is the best way to fit a nice effect on the bullet of my game
the game is a 3D ship shooter

i would like that the basic bullets are a sort of bright sphere, with the center white and going far from the center it become blue
I mean with a sort of tail that lost the color from white to blue

In the beginning I was thinking to create a flat square that with the billboarding was alway in the direction of the camera
and add to it a texture wiht the shape of a sphere

I have also created a simple particle engine to create more square one over the other that was moving from the center in the original direction of the bullet
so using then GL_BLEND function the sum of the color was white in the center and in the same time i was thinking that apply also this particles a sort of tail effect was created

I created it and the result was no so amazing has i was thinking,

do u have any other idea to implement this kind of effect?

also what is the best shape that as to be drow in the texture to create this effect